It's actually not that hard to find recent user manuals online, using Google. But the MakeUseOf blog has linked to a site that not only provides access to a bunch of manuals in one convenient place, but also allows you to register and then store all of your virtual manuals in a "filing cabinet."
And, like many websites these days, the The User Manual Site is social and interactive, maintaining a community message board where you can ask for help and tips from other consumers who are using the same product that you are.
These features make it worth checking out, and as you acquire new devices, adding those manuals to your online file. If they don't have a manual you need, you might be able to find it elsewhere. There are other user manuals sites, like http://www.usersmanualguide.com/ and http://www.user-manual-search.com/default2.aspx, but when you're looking for manuals, the best way to find them is often to simply Google the name of the manufacture, the model number, and the word "manual."